1. Field of the Invention
The present invention relates to a manufacturing method for a filter substrate that is used in a micro analysis device, such as a microreactor, a chemical-chip, a bio-chip, or a nano-chip, which has a micro structure as part of its constituent members, such as a flow passage, a reaction tube, a reaction tank, an electrophoresis column, a chromatographic column, or a membrane separation mechanism.
More specifically, the present invention relates to a manufacturing method for a micro chemical device that includes two members bonded together in which a groove or comparable recessed portion is formed on a substrate surface of one member.
Furthermore, the present invention relates to devices that can be manufactured by using the above methods. For example, the present invention relates to an inkjet recording head used to perform recording with a droplet of ink or other liquid discharged onto a paper or other recording material, and also relates to a manufacturing method for the inkjet recording head.
2. Description of the Related Art
A micro analysis device, which uses a very small amount of solution to cause a reaction or to perform separation or analysis, is composed of a smooth substrate overlaid with a member having a micro flow passage formed therein. The smooth substrate has an inlet and an outlet for the solution. The micro flow passage is formed on the member by chemical processing or energy ray treatment. Then, the smooth substrate and the member are bonded together by using ultrasonic wave, heat, pressure, or chemical processing.
In general, the substrate is made of an inorganic material, such as silicon, silica glass, boron silicate glass or ceramic, or an organic material, such as plastic materials including polycarbonate and polyacrylamide, silicone rubber, or silicon resin. A typical chemical processing is a dry etching or a wet etching. An energy ray treatment can be realized by using a laser or ion beam. The flow passage width of a micro flow passage is generally in a range from 40 μm to 500 μm, although it is dependent on the usage of the device. The depth of the flow passage is in a range from 0.6 μm to 500 μm.
In a structural body having such a flow passage formed therein, it is necessary to provide a filter in the flow passage so as to remove or separate foreign particles contained in the solution flowing in the flow passage or so as to separate such substances by electrophoresis. As a method for forming a filter, it is possible to employ a method of filling a part of the flow passage with gel, polymer, or zeolite with reference to the size of substances to be separated, or a method of providing a plurality of columnar structural bodies in the flow passage that are formed by dry etching or wet etching so as to arrange a physical filter.
An inkjet recording head is a structural body that requires a filter formed in the liquid passage. In general, the inkjet recording head has a plurality of discharge pressure generating portions, each including a fine discharge port (i.e., an orifice), a liquid flow passage connected to the discharge port, and a discharge pressure generating element provided partly in the liquid flow passage. The discharge pressure generating element is constructed from, for example, an electrothermal transducer.
Japanese Patent No. 3143307 discloses a related manufacturing method for an inkjet recording head. According to this manufacturing method, a mold of a liquid flow passage is formed with a dissoluble resin on a substrate on which a discharge pressure generating element is formed. Subsequently, a coating resin containing an epoxy resin that is in a solid state at ordinary temperatures is dissolved in a solvent. This solution is coated on the dissoluble resin layer by solvent coating techniques. Thus, a coating resin layer that forms a flow passage wall separating liquid flow passages is molded. Subsequently, a discharge port is formed in the coating resin layer. Finally, the dissoluble resin layer is eluted and removed.
Furthermore, Japanese Patent Application Laid-open No. 10-95119 and Japanese Patent Application Laid-open No. 10-34928 disclose an inkjet recording head and its manufacturing method, according to which the height of a flow passage located close to a supply port is set to be greater than the height of a flow passage located close to a discharge pressure generating element. According to these conventional manufacturing methods, a portion of a substrate corresponding to an area extending from the vicinity of the supply port to the vicinity of the discharge pressure generating element is recessed to assure a sufficient height of the flow passage in the vicinity of the supply port. As a result, the liquid flow passage has a large cross-sectional area. Accordingly, even if the discharge frequency (i.e., driving frequency) is increased, ink can be surely refilled into the flow passage after a droplet is discharged.
It is a recent trend that a higher resolution image and a higher quality image are demanded. To this end, the density of arrangement of discharge ports on an inkjet recording head tends to increase. Accordingly, if the cross-sectional area of the liquid flow passage is increased, the height of the liquid flow passage becomes greater than the diameter of the discharge port. Therefore, very fine foreign particles may enter the liquid flow passage and may clog the discharge port. On the other hand, it is conventionally known that a columnar filter can be provided between an ink supply port and a liquid flow passage.
Japanese Patent No. 3143307 discloses a manufacturing method for easily manufacturing this kind of columnar filter. However, this columnar filter cannot bring about sufficient filtering effects regarding a direction perpendicular to the direction of the liquid flow passage.
On the other hand, according to a filter forming method that requires a step of filling a part of the flow passage with gel, polymer, or zeolite, some time is necessary for such a filling step in each operation of the device. In addition, such a filler has nonuniformity in the molecular structure of holes. This brings about differences in the separation function, and, accordingly, it is difficult to obtain a desired size for the filler. Such a problem is not limited to the above-described inkjet recording head, and a similar problem will arise even in a micro analysis device.